Day 2

Setup

Mix.install([:kino])

input =
  Kino.Input.textarea("Paste input here",
    default: """
    forward 5
    down 5
    forward 8
    up 3
    down 8
    forward 2
    """
  )

input =
  input
  |> Kino.Input.read()
  |> String.split("\n", trim: true)
  |> Stream.map(fn
    "forward " <> x -> {:forward, String.to_integer(x)}
    "down " <> x -> {:down, String.to_integer(x)}
    "up " <> x -> {:up, String.to_integer(x)}
  end)

Part 1

{h, d} =
  input
  |> Enum.reduce({0, 0}, fn
    {:forward, x}, {h, d} -> {h + x, d}
    {:down, x}, {h, d} -> {h, d + x}
    {:up, x}, {h, d} -> {h, d - x}
  end)

h * d

Part 2

{h, d, _aim} =
  input
  |> Enum.reduce({0, 0, 0}, fn
    {:up, x}, {h, d, aim} -> {h, d, aim - x}
    {:down, x}, {h, d, aim} -> {h, d, aim + x}
    {:forward, x}, {h, d, aim} -> {h + x, d + aim * x, aim}
  end)

h * d